tztetait 
6 hr 30' 
t2f2f2t ft 
o>il on' 
24hr 30' 
♦ it 
^ol. on' 
48 hr 30 
96hr 
FIGURE 16. Treatment schedule to determine time course of recovery 
from suppression following the multiple injection subchronic 
treatment. In all cases rats were sacrificed at 30 minutes after 
the last injection in a series. The dose of cocaine for all 
treatments was 30 mg/kg. Six groups of rats were treated: 
(1) a single injection of saline or (2) cocaine; (3) the subchronic 
series (i.e., four injections of cocaine at 2-hour intervals); (4) 
the subchronic series and 24 hours later a challenge dose of 
cocaine; (5) the subchronic series with challenge at 48 hours; 
and (6) the subchronic series with challenge at 96 hours. 
causing an exaggeration of ongoing dopaminergic activity, only potentiating 
processes that are already in place. Thus, to some extent, induction and 
suppression of IEG expression are likely to be normal components of the 
biochemical repertoire accompanying dopaminergic neurotransmission. This 
idea is supported by our Northern and Western blot data, which usually show a 
low, but detectable level of c -fos mRNA and Fos-immunoreactive proteins in 
basal state striatum. Modulation of expression either up (the usual case) or 
down is possible. A similar situation is seen for NGFI-A (not shown). However, 
the basal expression of NGFI-A mRNA is much higher than for c -fos, and large 
amounts of NGFI-A protein can be detected in control brain nuclear extracts. 
These data suggest that induction of NGFI-A, unlike c -fos, occurs on a fairly 
high level of constitutive expression. 
203 
